1. Field of the Invention
The invention relates to a method and device for de-interlacing image signals, and to a display apparatus comprising such a de-interlacing device.
2. Description of the Related Art
De-interlacing is a basic requirement for practically all video scanning format conversions. Since perfection under all circumstances is impossible to achieve, many different algorithms have been proposed, ranging from simple spatial de-interlacing methods to the advanced motion compensated (MC) ones.
Many of the non-MC de-interlacing algorithms perform reasonably well on a limited set of sequences, but can suffer from annoying artifacts on another type of sequences. A nice overview is presented in Ref. [2] in the List Of References. For example, the field insertion algorithm is the best de-interlacer for stationary image parts, but is the worst for non-stationary image parts. Motion compensation can provide better results on moving images, but the algorithm remains very fragile, i.e., the performance degrades rapidly to unacceptable levels if the motion compensation is not completely correct. A de-interlacer that can better cope with both stationarities and non-stationarities is the vertical-temporal median filter. This median filter de-interlacer inherently switches between field insertion and line repetition. However, due to its non-linear nature, it introduces harmonics (and therefore alias) in image parts containing vertically high frequencies. The vertical-temporal linear filter, as also commercialized by Genesis (See Ref. [1]), is better suited for sequences containing vertical high frequencies, but will not preserve edges as well as the median, while moving details may cause echoes in the image. In the literature, some proposals have been presented that explicitly switch or fade between multiple algorithms (see also Refs. [3]-[6]). The decision between the different algorithms is either determined by motion detection or edge detection. A very reliable detector is, however, difficult to design, as also mentioned in Ref. [2]. A more robust alternative would provide an attractive option.
It is, inter alia, an object of the invention to provide an improved de-interlacing. To this end, the invention provides a de-interlacing method and device, as well as a display apparatus incorporating such a device.
In a method of de-interlacing video data in accordance with a primary aspect of the present invention, at least three different de-interlacing algorithms are applied on the video data to obtain at least three de-interlaced signals, no majority of de-interlacing algorithms copying a single spatio-temporally neighboring pixel to the interpolated position, and the at least three de-interlaced signals are order statistical filtered to obtain an output signal.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.